init: improve corrupted/empty settings file error msg

The preceding "Unable to parse settings file" message lacked
the necessary detail and guidance for users on what steps to
take next in order to resolve the startup error.

Co-authored-by: Ryan Ofsky <ryan@ofsky.org>

Author: furszy

src/common/settings.cpp

@@ -81,7 +81,9 @@ bool ReadSettings(const fs::path& path, std::map<std::string, SettingsValue>& va
 
     SettingsValue in;
     if (!in.read(std::string{std::istreambuf_iterator<char>(file), std::istreambuf_iterator<char>()})) {
-        errors.emplace_back(strprintf("Unable to parse settings file %s", fs::PathToString(path)));
+        errors.emplace_back(strprintf("Settings file %s does not contain valid JSON. This is probably caused by disk corruption or a crash, "
+                                      "and can be fixed by removing the file, which will reset settings to default values.",
+                                      fs::PathToString(path)));
         return false;
     }
 

src/test/settings_tests.cpp

@@ -99,7 +99,9 @@ BOOST_AUTO_TEST_CASE(ReadWrite)
     // Check invalid json not allowed
     WriteText(path, R"(invalid json)");
     BOOST_CHECK(!common::ReadSettings(path, values, errors));
-    std::vector<std::string> fail_parse = {strprintf("Unable to parse settings file %s", fs::PathToString(path))};
+    std::vector<std::string> fail_parse = {strprintf("Settings file %s does not contain valid JSON. This is probably caused by disk corruption or a crash, "
+                                                     "and can be fixed by removing the file, which will reset settings to default values.",
+                                                     fs::PathToString(path))};
     BOOST_CHECK_EQUAL_COLLECTIONS(errors.begin(), errors.end(), fail_parse.begin(), fail_parse.end());
 }
 

test/functional/feature_settings.py

@@ -53,7 +53,7 @@ def run_test(self):
         # Test invalid json
         with settings.open("w") as fp:
             fp.write("invalid json")
-        node.assert_start_raises_init_error(expected_msg='Unable to parse settings file', match=ErrorMatch.PARTIAL_REGEX)
+        node.assert_start_raises_init_error(expected_msg='does not contain valid JSON. This is probably caused by disk corruption or a crash', match=ErrorMatch.PARTIAL_REGEX)
 
         # Test invalid json object
         with settings.open("w") as fp: